The invention relates to a multilayer capacitor having a capacitor element in which dielectric layers and internal electrodes are alternately stacked and more particularly to a shape of a capacitor element.
Recently, electronic equipment has rapidly advanced in size reduction because of sophistication of ICs (integrated circuits), LSIs (large scale integrated circuits) and so on. With the advance in size reduction, a capacitor that is an electronic component is also advancing in size reduction, and thus a demand for a multilayer capacitor is growing sharply. For example, known is a multilayer capacitor comprising a capacitor element in which dielectric layers and internal electrodes are alternately stacked and also having terminal electrodes formed in the capacitor element. The capacitor element is generally formed in the following manner using a dielectric paste containing a dielectric material blended with an organic vehicle and an internal electrode paste containing a conductive material blended with an organic vehicle: that is, the dielectric paste and the internal electrode paste are alternately stacked, then the stacked pastes are integrated by applying pressure to the pastes, and finally the integrated pastes are fired.
In the case of the above-mentioned capacitor element, the internal electrode has to be made of a material that does not react with a material of the dielectric layer even if the internal electrodes are fired simultaneously with the dielectric layers, because the internal electrodes integrated with the dielectric layers are fired simultaneously. Therefore, a noble metal such as platinum (Pt) or palladium (Pd) has been heretofore used as the internal electrode. However, the noble metal is expensive and results in a rise in the price of the multilayer capacitor. Therefore, studies are conducted for the purpose of using an inexpensive base metal as the internal electrode, so that a dielectric capable of being fired in a reducing atmosphere in which nickel (Ni) does not oxidize is developed, thereby making it possible to use nickel as the internal electrode and thus achieving a substantial reduction in cost.
When nickel is used as the internal electrode, the internal electrode is, however, prone to break because the internal electrode becomes spherical and thick as sintering proceeds. Thus, a problem exists: that is, the multilayer capacitor expands in a stacking direction and a width direction, so that cracks occur in the multilayer capacitor. This problem becomes more noticeable as the number of dielectric layers increases, and the problem has been serious particularly in recent years in which, to meet demands for a smaller size and a larger capacity, the dielectric layer has become thinner and increased in number and therefore the number of dielectric layers has increased.
As the related art pertaining to the internal electrode paste, addition of a carbon compound is described in, for example, Japanese Patent Application Publication No. Hei 2-94618, but the addition of the carbon compound takes place in order to inhibit oxidation of the internal electrode, and this publication gives no description about the correlation between the addition of the carbon compound and the occurrence of expansion and cracks of the multilayer capacitor.
The invention is designed to overcome the foregoing problem. It is an object of the invention to provide a multilayer capacitor capable of preventing the occurrence of cracks by inhibiting the multilayer capacitor from expanding in the stacking direction or the width direction.
There is provided a multilayer capacitor of the invention comprising a capacitor element in which dielectric layers and internal electrodes are alternately stacked, wherein an expansion coefficient x of the capacitor element in a stacking direction lies between xe2x88x920.05xc3x97i (%) and 0.05xc3x97i (%) inclusive, where i denotes the number of dielectric layers, each of which is sandwiched between the internal electrodes.
There is provided another multilayer capacitor of the invention including a capacitor element in which dielectric layers and internal electrodes are alternately stacked, wherein the expansion coefficient x of the capacitor element in the stacking direction lies between xe2x88x920.10 (%) and 0 (%) inclusive.
In the above-described multilayer capacitors of the invention, the expansion coefficient x of the capacitor element in the stacking direction falls within a predetermined range, so that the occurrence of cracks is prevented, and therefore a fraction defective is reduced.
Preferably, in the multilayer capacitor of the invention, the expansion coefficient x lies between xe2x88x920.05xc3x97i (%) and 0 (%) inclusive. Preferably, in the above-described multilayer capacitors of the invention, the capacitor element has the dielectric layer in an outermost portion in the stacking direction, and the dielectric layer located in the outermost portion has a thickness of 100 xcexcm or less. In the above-described multilayer capacitors, the internal electrode may include nickel.
The capacitor element is obtained by stacking and firing a dielectric paste layer containing a dielectric material and an internal electrode paste layer containing a conductive material, and the internal electrode paste layer may comprise at least one of a carbon compound and a lithium-containing compound. Preferably, the internal electrode paste layer contains the carbon compound in such a manner that the content of carbon lies between 0.5 and 16 parts by weight inclusive to 100 parts by weight of a metallic element in the conductive material. Preferably, the internal electrode paste layer contains the lithium-containing compound in such a manner that the content of lithium (Li) lies between 0.005 and 10 parts by weight inclusive to 100 parts by weight of the metallic element in the conductive material. Preferably, the lithium-containing compound is lithium-containing salt.
There is provided still another multilayer capacitor of the invention comprising a capacitor element in which dielectric layers and internal electrodes are alternately stacked, wherein an expansion coefficient y of the capacitor element in a width direction lies between xe2x88x920.05xc3x97i (%) and 0 (%) inclusive, where i denotes the number of dielectric layers, each of which is sandwiched between the internal electrodes.
In the above-mentioned multilayer capacitor of the invention, the expansion coefficient y of the capacitor element in the width direction falls within a predetermined range, so that the occurrence of cracks is prevented, and therefore the fraction defective is reduced. In the multilayer capacitor, the internal electrode may include nickel.
The capacitor element is obtained by stacking and firing a dielectric paste layer containing a dielectric material and an internal electrode paste layer containing a conductive material, and the internal electrode paste layer may contain a lithium-containing compound. Preferably, the internal electrode paste layer contains the lithium-containing compound in such a manner that the content of lithium lies between 0.005 and 10 parts by weight inclusive to 100 parts by weight of the metallic element in the conductive material. Preferably, the lithium-containing compound is lithium-containing salt.
Other and further objects, features and advantages of the invention will appear more fully from the following description.